This invention relates generally to internal combustion engines, and more specifically to the cylinder liners mounted in the engine cylinder block. Still more specifically, the invention concerns the coatings applied to the inside surfaces of the cylinder liners for making them resistant to wear and seizure.
Some internal combustion engines have cylinder blocks made of aluminum with a view to lightness and heat conductivity. However, aluminum is too soft to use as cylinder wall material. It would wear very rapidly. A well known solution to this problem is the use of cast iron cylinder liners. These are, in fact, sleeves that are either integrally cast into the cylinder block or installed later. The cylinder liners generate much heat as they make direct sliding contact with the pistons, so that they must be cooled by water or air. However, as is well known, as much as one third of the total heat generated by the combustion of the fuel has usually been wasted by the forced cooling of the engine. The reduction of this cooling loss will result not only in a decrease in energy loss but also in the smaller space requirement of the cooling system.
A dissipation of less heat from the cylinder liners necessitates the protection of their inside surfaces against overheating. Various coating materials have been suggested which are believed to be capable of making the cylinder liner surfaces resistant to seizure and abrasion. Such suggested materials include chromium carbide, titanium carbonate and oxide, chromium oxide, and alumina titania. However, the coating of these materials on the complete inside surfaces of the cylinder liners adds considerably to the manufacturing costs of the engines. For this reason some of them have won only a limited acceptance, and others none at all, among engine manufactures.